"Stewart Coffin designed this puzzle in 1990. This puzzle is well described in his 1992 version of Puzzle Craft. It is made of ten identical pieces, one key and one augmented piece. Assembling and disassembling the puzzle requires shifting the pieces back and forth in order to insert or remove the next piece. Mr Coffin considers this puzzle to be difficult to solve, and step by step instructions are also given in Puzzle Craft. He considers the 12 Piece Separation one of his top favorite designs. It is number 85 in his design numbering list. He made about 30 of them from 1988 to 1992." -Eric Fuller